1. Field of the Invention
The present invention relates to an ink jet recording apparatus and a recovering mechanism for an ink jet head, and particularly relates to a recovering unit for maintaining the ink jet head of an ink jet recording apparatus in a normal ink ejection state or recovering the ink jet head to the normal ejection state.
2. Description of the Related Art
Among the conventional ink jet recording apparatus, there is one which has a recovering pump arranged for the purposes of maintaining an ink jet head in a normal ink emission state or recovering the ink jet heads to the normal state when clogging takes place in an orifice or orifices. Ink is sucked out of the orifice or orifices, using vacuum produced by the recovering pump. Examples of such technique include the use of a tube pump as the recovering pump (for instance, see Japanese Laid-Open Patent Application Nos. 73352/1991 and 73354/1991. The tube pump produces vacuum by changing a volume in each flexible tube.
FIGS. 1A and 1B diagrammatically illustrate the tube pump. An opening of a cap 30 is brought into contact with a ink jet head 1 to perform capping of a face 1A on which orifices are formed. The cap 30 is provided in the rear side thereof with another opening, which is connected to a tube 3 as a member of the tube pump. A pressurizing roller 5 is provided to each tube 3 for pressurizing, and a shaft 5A thereof is rotatably supported to a guide roller 4. The guide roller 4 is rotatably mounted at a shaft 4A thereof to a pump base 6. The pump base 6 has an arcuate groove 6A formed concentrically with the shaft 4A of the guide roller 4.
When in such a construction, the guide roller 4 is rotated in the direction of the arrow a by a drive mechanism (not shown), the pressurizing roller 5 on the guide roller 4 is brought into contact with the tube 3 in the portion X in FIG. 1A to press the tube 3, so that the tube is resiliently deformed to bring the cross-sectional area of the interior thereof at the portion X to substantially naught. The guide roller 4 is further rotated in the direction of the arrows a from this state. This makes the pressurizing roller 5 to rotate in the direction of the arrow b in a following manner, collapsing the tube 3. The pressurizing roller 5 is temporarily stopped at a portion Y of the tube 3 as shown in FIG. 1B. During this operation, negative pressure is produced in the face 1A of the head 1 due to change in volume of the interior of the tube while the roller 5 presses the tube 3 between the portions X and Y thereof. The negative pressure enables suction of ink from the orifices. A waste ink container 7 is arranged downstream of the tube 3 for containing ink sucked from the orifices.
Such a tube pump is advantageous in that it is simple in construction and it is capable of constitute a small and low cost suction recovering unit. The inventors however have found that the tube pump can raise problems below.
The amount of overlapping of the pressurizing roller 5 with the corresponding tube 3 (the amount of penetration of the pressurizing roller 5 upon the tube 3) depends on the distance from the axis of the guide roller 4 to the axis of the pressurizing roller shaft 5A, the outer diameter of the pressurizing roller 5, the shape of the arcuate groove 6A concentric with the guide roller 4, the thickness of the tube 3, plays to these members, etc. The minimum amount of penetration which bring the cross-sectional area of the interior of the tube 3 to substantially naught must be determined in view of a tolerance of each of the members. In the case where the amount of penetration of the pressurizing roller 5 increases due to the tolerance, the torque to drive the pump, that is, the torque to rotate the guide roller 4 in the direction of arrow a, must be also increased. This necessitates the torque of a pump drive motor to be enlarged, and therefore it is like to raise a cost of the motor. In the case of excessively large amount of penetration, wear of the tubes is accelerated, durability of the tubes is deteriorated, and hence the tubes are liable to be broken.
For the purpose of obtaining a small and low cost recording apparatus, in the case where a motor is commonly used as the pump drive motor and a recording medium feeding motor (vertical or subscanning motor) or a carriage drive motor (horizontal or main scanning motor), the following problems are likely to be produced: the motor can be stepped out due to change in torque at an instant when tubes 3 are pressed by the pressurizing roller 5 or are released from the pressurizing rollers 5; accuracy of feed of the recording medium is adversely affected; the picture of printing is deteriorated in quality due to nonuniform scanning.
In the case where a plurality of heads are used, a plurality of tubes 3 and pressurizing rollers 5 are provided. Thus, an increase in the amount of penetration according to the tolerance of each component become larger as the increase of the number of the heads. This makes influences of the problems previously described larger.